The mode of regulation of synthesis of hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) in cultured human cells will be studied. The enzyme has been purified from human erythrocytes and antiserum has been prepared to it in rabbits. The antiserum is being used to develop a quantitative analysis for HGPRTase protein in cell extracts. Human cells mutated in expression of HGPRT are being selected in culture. Synthesis of enzyme in these cells and in normal cells exposed to various metabolic conditions will be measured. The intent is to accumulate sufficient data regarding synthesis of the enzyme to reveal whether that synthesis is regulated at transcription or translation, by "positive" or "negative" factors. Synthesis of the enzyme and enzyme protein levels will also be studied in cells from gout patients and cells from individuals afflicted with the Lesh-Nyhan syndrome of HGPRTase deficiency.